by Jim Eldridge
Under the terms of the Versailles Treaty, Germany had to formally accept responsibility for the war. It also lost substantial territories: not only its colonial territories overseas (such as those in Africa) but also some of its territories on its own borders (such as those bordering Poland and Austria). Germany also had to pay £6.6 billion (equal to £282 billion in current terms) in compensation to the victorious countries. There were some among the Allies (including Alan’s tutor at Cambridge, the economist John Maynard Keynes) who felt that this compensation was too much, and would lead to great hardship and resentment among the Germans, and could lead to Germany going to war again. But the French Government, in particular, insisted on the compensation being paid.
Those in the German military who were determined to make Germany powerful again realised that if they were to take their chances on another war of conquest, they needed their military to be far superior to any possible enemy, and also that they needed improved intelligence and secret communications to prevent the enemy from finding out their plans and operations.
In 1923 Arthur Scherbius, a German inventor and engineer, invented a machine which could be used for high-security communications. He called this machine, and the code it used, Enigma – ‘mystery’.
In a simple code or cipher, a letter can be represented by another letter, or a number. For example, in a code where every letter is moved along one space, A becomes B, B becomes C, C becomes D, and so on, and thus the word BAD in code becomes CBE. The problem with simple codes is that they can be broken, and relatively quickly.
The Enigma machine was an electro-mechanical machine, which used rotors to send and receive coded messages. It contained three rotors with 26 electrical contacts on each side (one for every letter of the alphabet). When a key on the keyboard was pressed, an electrical current was sent through the set of rotors. In this way encrypted messages were created and sent by wireless.
In order to decode the messages sent through Enigma, the person receiving the coded message had to know how to set the rotor wheels of the receiving machine so that they matched the position of the sending machine. The positions of the rotors were sent out using a separate code key, and these code keys were listed in a code book kept by all Enigma operators.
Because these codes changed frequently, and because the machine used a mechanical encryption system that had trillions of possible solutions, a message sent from an Enigma machine could really only be deciphered by someone who had not only another Enigma machine but also the current code.
To give you an idea of how hard the Enigma code was to break: three rotors, each with 26 possible correct answers, means that for each encrypted letter there are 26 x 26 x 26 = 17,576 possible solutions. So the possibility of working out the right letter of the code was tiny.
In addition, the Enigma machine had another safeguard: the rotors could be taken out and their sequence altered. When the original 17,576 solutions are multiplied by six (the number of possible wheel orders), that gives 105,456 ways the originating scrambler code could be set up.
By the 1930s, countries who had been enemies of Germany in the First World War had learned about the existence of Germany’s Enigma machine and its code, and their intelligence agencies set to work to try and discover how to break the code. They were worried about the rise of Adolf Hitler and his Nazi party. If Hitler came to power and launched another war, then the Enigma code would give Germany a major advantage in secret communications.
In 1932, French agents managed to get hold of an instruction manual for the Enigma machine. They passed it on to the Polish secret service. France and Poland, as countries who shared borders with Germany, saw themselves as most at risk in the event of another war breaking out. The Poles put mathematicians to work on trying to discover from this instruction book how the Enigma machine was wired, and how the rotors worked, and to try and break the code from messages they intercepted.
By the mid-1930s, using the instruction book and mathematical theory, the Polish mathematicians had cracked the Enigma code. Once the Germans became aware of this, in 1938, they developed an even more complicated version of the Enigma machine. The Polish mathematicians found it impossible to break this one at first. But then they came up with a possible answer: using the original Enigma instruction book, they built a machine made up of Enigma rotor assemblies connected together. They called this machine a Bombe.
Like the Enigma machine, the Bombe was an electro-mechanical device. Its task was to identify possible initial positions of the Enigma rotor cores, and the specified series of letters in the correct order, as produced by a set of rotor wheels. In other words, it was intended to be a mirror of the Enigma machine, which would translate the coded gibberish the Enigma machine produced back into the original words.
Using the Bombe, the Poles were able to continue decoding intercepted Enigma messages.
However, once the Germans became aware their messages were being intercepted, they simply added more rotors to their own Enigma machines, going from the original three-rotor version to a four-rotor version, and then a five-rotor version. The more rotors being used to generate the coded message, the greater were the odds against the code being cracked. The Enigma code had become virtually unbreakable.
6
Bletchley Park
So far, the battle between the Germans and the Poles to solve the Enigma code might seem to be just a clash of mathematicians battling for supremacy, trying to outdo one another in an intellectual game – a kind of super-chess. But, once war was declared in September 1939 between Germany and her enemies, especially Britain, it became a battle where millions of lives were at stake.
The entire German military machine depended on Enigma for secret communications, details of troop movements and plans of attack, but the aspect of Enigma that would affect Britain most was related to the German Navy communications.
Every ship in the German Navy had an Enigma machine on board to receive coded intelligence and instructions. This included the small fleets of submarines, called U-boats, that patrolled the Atlantic. Their aim was to stop merchant shipping between America and Britain. Britain is an island nation and at the start of the war it wasn’t able to produce enough food, fuel, weaponry or ammunition for its needs. So, although at the start of the war America was neutral, most of Britain’s much-needed supplies came from America. The German plan was to sink these cargo ships to prevent them from reaching Britain. Without these vital supplies, Germany felt confident that Britain would be forced to surrender.
This fear was also shared by the British Prime Minister, Winston Churchill. If Britain could not stop the attacks on the supply convoys by the German U-boat fleets (known as ‘wolf packs’), then the country would run out of vital supplies and the war would be lost.
The convoys of cargo ships bringing these supplies across the Atlantic were protected by Royal Navy destroyers, but these were prone to attack from the deep by the wolf packs, who attacked swiftly with their torpedoes, sinking the ships and then vanishing.
The U-boats received details of their targets through the Enigma machine on board, and kept in touch with each other the same way. If the wireless transmissions between the U-boats and their HQ could be unscrambled and deciphered, then the Allies would know what their positions were, which was their next intended target, and when an attack was planned for. They could then take countermeasures to protect the convoy, with warships and planes bombing the U-boat positions. Without that knowledge, every convoy was a row of sitting ducks on thousands of miles of ocean, ripe for a surprise attack.
Cracking the German Naval Enigma code that organised the deadly U-boat wolf packs was absolutely vital if Britain was to survive.
On 4 September 1939, the day after war had been declared between Britain and Germany, Alan Turing reported for duty at Bletchley Park in Bedfordshire. He was 27 years old.
Bletchley Park was a large mansion house set in extensive grounds. Much of the code-breaking work would be carri
ed out in the long single-storey wooden huts that had been set up in the grounds around the main house. Alan was put in charge of Hut 8, where the aim was to crack the German Navy’s Enigma coded messages.
Although Alan’s intellect had developed since Sherborne and Cambridge, his social skills hadn’t. By all accounts he was a solitary person outside work, and cared little for his appearance. There are reports of him keeping his trousers up with string tied round the waist, rather than a belt or braces. A colleague at Bletchley described Alan as ‘a tallish dark-haired powerfully built man with sunken cheeks and deep-set blue eyes. He wore unpressed clothes and picked at the flesh around his fingernails until they bled. He stammered and would often fall into long silences. He rarely made eye contact with anyone.’
In the 21st century, someone in such an important position exhibiting these unusual traits of behaviour would probably be examined by psychologists and counsellors to find out why he acted like that, and if he was odd enough to present a danger to the establishment. In recent years, people have tried to understand Alan’s rather anti-social manner, suggesting a variety of reasons for how he behaved. Was it because of his separation from his parents at a very early age? The fact that he was gay, and therefore emotionally isolated, because he had to control his feelings so as not to fall foul of the law? Or simply the fact that he felt different because he was cleverer than most people he came into contact with?
It’s fascinating to speculate on this now. But in 1939 there was a war on, and nobody had time to worry about what people like Alan were thinking. Britain was in a desperate situation, and it needed everyone to help if the country was going to survive.
The people sent to work at Bletchley came from a variety of interests. There were code-breakers, including mathematicians like Alan, and those with a proven ability to solve puzzles, including chess masters, people who solved cryptic crosswords quickly, and those with similar skills. There were also linguists (for translating intercepted messages in German and other languages), as well as large numbers of people who would intercept and transcribe the wireless transmissions and pass them on to the code-breakers.
One of the first things Alan and the other code-breakers did was to look at the work of the Polish code-breakers, and their code-breaking Bombe machines. They quickly realised that, although these machines had worked well at breaking the early versions of the Enigma code, the additional codes the German had built into their machines meant that any Bombe built to try and crack it would have to be on a much larger scale than any of the previous Bombes. And, even if they managed to build a big enough Bombe machine, all the Germans had to do was add another rotor or more to their Enigma machine, and the codes would become virtually unbreakable once again, especially considering how fast they had to be deciphered to stop the U-boat attacks in the Atlantic.
When the scale of the problem became apparent, especially when set against its urgency as more and more supply ships were lost, some people in British Intelligence thought the best way to solve the problem was simply to get hold of an Enigma machine. One of these was a Naval Intelligence Officer, Lieutenant Commander Ian Fleming (later to create James Bond), who came up with a plan called Operation Ruthless to try and capture an Enigma machine.
At this time, Fleming was personal assistant to the Director of Naval Intelligence, Rear Admiral John Godfrey. As part of his duties, Fleming visited Bletchley Park twice a month to liaise with Alan Turing and the other code-breakers, and when he outlined his plans for getting hold of an Enigma machine, Alan gave Fleming his enthusiastic support.
This is Fleming’s own wording for his plan, which he called ‘Operation Ruthless’, and which he sent to Rear Admiral Godfrey in September 1940:
I suggest we obtain the loot [an Enigma machine] by the following means:
1. Obtain from Air Ministry an air-worthy German bomber.
2. Pick a tough crew of five, including a pilot, wireless telegraph operator and word-perfect German speaker. Dress them in German Air Force uniform. Add blood and bandages to suit.
3. Crash plane in the Channel after making SOS to [German] rescue service.
4. Once aboard rescue boat, shoot German crew, dump them overboard, bring rescue boat with loot back to English port.
F. 12.9-40. (Fleming. 12 September 1940.)
Fleming had volunteered to be one of the crew of the captured German airplane on this mission, but because of his connection with Bletchley Park it was felt that it was too great a risk if he was captured by the Nazis and interrogated.
A captured German Heinkel was made ready for the mission, and a crew of German-speaking British servicemen were assigned. The plan was to be put into operation at the start of October because it was known that the codes for Enigma were changed at the beginning of every month.
At the start of October, Fleming and his volunteers, along with the Heinkel aircraft, assembled at Dover, waiting for the next German bombing raid, which they would use as cover to launch their own German bomber over the English Channel. However, at the last moment the mission was cancelled.
Alan Turing was so furious at the cancellation that he stormed into the office of his immediate superior at Bletchley Park, Frank Birch, to complain. Birch wrote in a report on 20 October 1940:
Turing and Twinn [Peter Twinn, another mathematician on the team] came to me like undertakers cheated of a nice corpse two days ago, all in a stew about the cancellation of Operation Ruthless.
Fleming based his fictional creation of James Bond on himself and his own career in Naval Intelligence. It is interesting to speculate whether the character of Q in the James Bond novels was based on the scientific boffins like Alan at Bletchley Park.
7
Breaking the Code
With the cancellation of Operation Ruthless, there was little chance of Britain getting hold of a real Enigma machine. Time was running out for Britain as the deadly U-boat attacks on the convoys sank more ships and destroyed many more essential supplies.
Many of the scientists at Bletchley Park felt that the Enigma code simply couldn’t be cracked. Because it was so complex and with so many permutations, it was thought to be literally unbreakable. Possibly the only two who considered it could be broken were Alan and Frank Birch, the head of Bletchley’s Naval Intelligence division. They both believed that the only way to crack the German Naval Enigma code was to design and build a new version of the Bombe. And to do that, they would need to design and build a thinking mathematical machine, essentially a continuation of Alan’s previous work.
Alan designed a new and advanced version of the Bombe, taking on board important suggestions made by another of his fellow code-breakers at Bletchley Park, Gordon Welchman, who was in charge of Hut 6, responsible for cracking the codes used by the German Army and Air Force. The actual machine was built by an engineer called Harold Keen, working closely with Alan and Gordon.
The way that Bletchley Park worked was as follows: clerks listened in to the wireless traffic between the German commanders and their outposts (including the U-boats) and transcribed the messages, which were in code, and in German.
These messages were passed to the code-breakers, who ran the coded messages through the Bombe machines to try and make the message intelligible, rather than a mass of gibberish.
The problem with cracking the Enigma code was that, although Bletchley intercepted thousands of coded messages every day, the sending machine used an encryption system that had trillions of possible solutions, and the key code was changed constantly. In other words, the sheer volume of messages presented to the code-breakers was too large, not just for the code-breakers themselves, but for the Bombe. This meant that the process of trying to break the code was frustratingly slow, and also dangerously slow. The more time passed with the Atlantic convoys being lost, the more likely it was that Britain would be forced into surrender.
To try and speed the process up, Alan and the other code-breakers decided to concentrate their attentions on short repea
ted phrases in the coded messages. They knew that if every German outpost – whether at sea, or on land, or in the air – was sending the same kind of message regularly, then it would very likely be a standard phrase such as ‘Nothing to report’, ‘Weather for the night’, or even ‘Heil Hitler’. Alan and his fellow code-breakers called these short formulaic messages ‘cribs’.
Alan also decided to work on a process of elimination: that is, it is easier to disprove a hypothesis than to confirm one. Disproving some possible answers, and thereby eliminating them from any equation, would help reduce the potential workload required in the code-breaking.
Using these methods when examining the coded messages, Alan spotted a weakness in the German Naval Enigma. The cribs such as ‘Wetter fur die nacht’ (‘Weather for the night’), could be translated by guesswork and could be exploited to follow logical chains, each of which offered billions of possible Enigma settings. If one of these chains led to a contradiction, the billions of corresponding settings on that chain could be eliminated.
However, the odds against finding an answer were still enormous, and a huge number of workers were needed at Bletchley – listeners, transcribers, typists – to examine every coded message that was intercepted, extract these cribs and run them through the Bombes. It was soon realised that the task of sorting through every message and extracting the cribs was too big for the existing numbers of staff. More workers were needed. The problem was that the skilled workers needed to carry out the work were often already at work in other vital areas important to the war effort, so the requests from the Senior Commanders at Bletchley to the War Office for more staff were constantly turned down.